1. Field of the Invention
This invention relates to a method of making hard boron nitride capable of being employed in surface coating of cutting tools, electronic materials, light emitting diodes and the like.
2. Discussion of the Background
Conventionally, as a synthesizing method of hard boron nitride employing a gas phase synthesizing method without using elevated temperature and high pressure, the following (1) through (6) methods have been tried.
(1) A pulse discharge is performed between a boron electrode which is sintered in a bar-like shape and a water-cooled copper electrode in a mixture gas of nitrogen and hydrogen, and activated boron and nitrogen are reacted and accumulated on a substrate (reactive pulse method).
(2) Hard boron nitride is synthesized by a hot gas phase reaction employing electron beam irradiation (electron beam gas phase reacting method).
(3) Molecular beam deposition is employed wherein borazine (B.sub.3 N.sub.3 H.sub.6) is the raw material and the raw material is accelerated under 1 through 3 KV (molecular beam method).
(4) Nitrogen molecular ions which are accelerated by approximately 30 eV, are injected, while performing electron beam deposition of boron (molecular beam method).
(5) Boron gas and nitrogen gas which are gasified by an electron beam, are ionized by thermions, which are accumulated on a substrate by biasing them (ionized deposition method).
(6) The other methods are the neutralized iron beam method, the laser pulse deposition method and the like.
However, since the film synthesized by the above methods, is a film composed of very fine particles of which grain size is not larger than 500 .ANG., there is no crystal wall and the film is mixed with h-BN, the film is unstable in air. Accordingly, the film is not regarded as the hard boron nitride film